DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 4AE0860A2611
Date: Wed, 11 Nov 2026 13:09:52 +0100
From: Wolfram Sang <wsa+renesas@sang-engineering.com>
To: phucduc.bui@gmail.com
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Simona Vetter <simona@ffwll.ch>, dri-devel@lists.freedesktop.org,
	linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] drm: shmobile: Fix white screen after resume when
 LCDC is stopped
Message-ID: <avRbEGoPh3bqR93f@ninjato>
References: <20260707093004.987846-1-phucduc.bui@gmail.com>
Precedence: list
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20260707093004.987846-1-phucduc.bui@gmail.com>

On Tue, Jul 07, 2026 at 04:30:04PM +0700, phucduc.bui@gmail.com wrote:
> From: bui duc phuc <phucduc.bui@gmail.com>
> 
> The LCDC on R8A7740 may show a completely white screen after resuming
> from suspend (s2idle or s2ram).
> 
> After resume, both Set A and Set B registers are reset to 0. As the
> Frame End interrupt is not generated while the controller is stopped
> (DO=0), the hardware register switching mechanism is not triggered.
> Consequently, Set A remains at 0x00000000 even though a valid Start
> Address is written to Set B, resulting in a white screen.
> 
> This is a timing-dependent race condition. In some configurations,
> debug options slow down the resume path enough for a Frame End
> interrupt to occur, which can mask the issue.
> 
> Fix this by priming both register sets with the Start Address while the
> controller is stopped, ensuring a valid base address is available
> immediately after resume.
> 
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: bui duc phuc <phucduc.bui@gmail.com>
> ---
> 
> Note:
> It was originally posted in March and has already received both 
> Reviewed-by and Tested-by tags. I'm resending it to bring it back 
> to attention in case it was overlooked.
> 
> Changes in v4:
>  - No functional changes.
>  - Resend.

Still not upstream? Who is the person to pick this up? This is a
valuable fix we surely want to have.